Cathode ray tube arrangement



Oct. 26, 1943. F. WOERNER 2,332,881

CATHODE' RAY TUBE ARRANGEMENT Filed Nov. 24, 1939 2 Sheets-Sheet 1 .7/5yen/0r Oct. 26, 1943. F. WOERNER 2,

CATHODE RAY TUBE ARRANGEMENT Filed Nov. 24, 1959 2 Sheets-Sheet 2 .70 uen/or Patented Oct. 26, 1943 OATHODE RAY TUBE ARRANGEMENT FriedrichWoerner, Berlin, Germany; vested in the Alien Property CustodianApplication November 24, 1939, Serial No. 305,967

3 Claims.

The present invention relates to arrangements more particularly fortelevision purposes comprising a cathode ray tubeprovided with aluminescent screen and means for deflecting the oathode ray to scan saidscreen.

The arrangement according to the invention is an improvement andmodification of the arrazigement described in the co-pending applicationSerial No. 239,153, filed November 15, 1938. In this prior applicationmeans are disclosed for preventing the negative ions from destroying theluminescent material at those parts of the screen which are hit by theions. Luminescent materials consisting of a sulphide have proved to beparticularly liable to the influence of the ions,

while, on the other hand, they are distinguished by a high luminousemciency and a colour of emitted radiation which is particularlysuitable for television purposes. The detrimental efiect caused by thenegative ions becomes remarkable especially when magnetic means are usedfor the deflection of the cathode ray in at least one direction.

In the case of a combined electrostatic and electromagnetic deflection,after a rather short period of operation, there is observed a dark lineon the luminescent screen which extends transversely through the imagefield parallel to the magnetic and electric lines of force. Whenmagnetic deflection takes place in both directions, a dark spot appearsat the centre of the screen.

It is an object of the present invention to provide improved means whichprevent the appearan'ce of the just described interference and at thesame time allow an undisturbed deflection and focusing of the cathoderay.

The present invention will be better understood from, and furtherfeatures of the invention will appear in connection with the followingmore detailed description and the accompanying drawings of which, in apurely diagrammatic fashion and by way of example,

Figure 1 represents the luminescent screen of a cathode ray tube showingtwo different lines drawn by the cathode ray when acted upon by theperiodical deflection in only one direction,

Figure 2 shows a substantially cross-sectional view taken in ahorizontal plane, of a tube according to the invention and the essentialparts of the external circuits necessary for operating the tube,

Figure 3 is a substantially cross-sectional view taken in a verticalplane and partly broken away, of a tube according to the invention,showing a Germany November 30, 1938 modification of the deflectingsystem of Figure '2 and some further circuit elements,

Figure 4 is a, section perpendicular to the tube axis of the tube ofFigure 3, taken substantially along the plane AA of Figure 3 and viewedfrom the side of the luminescent screen, and

Figure 5 is a view similar to Figure 4 showing I a modification.

In the-above cited prior application, a predeflecting condenserconsisting of the plates l-2 of Figure 2 is described which is-arranged,seen in the'direction of the electron beam, in front of the maindeflecting system, i. e., -the system which performs the periodicaldeflection of the ray for scanning the screen. As shown in Figures 2-and 3, the main system mayconsist of a condenser 4-5 for the purpose ofelectrostatic deflection and a pair of coils 24--25 for the purpose ofelectromagnetic deflection. The predefiecting condenser imparts to thecathode ray such a direction that the ray, when the main deflectingsystem is not in operation would impinge upon the edges of the screenbeyondthepicture area. By an additional direct current which is causedto flow through the main deflecting coils the ray is guided back to thecentre of the picture area. The ions respond only to i the electrostaticinfluence While the electrons are deflected by both the electrostaticand the electromagnetic fields. In this way the interfering eflect is.removed from the picture area.

When carrying out this method described in the prior application forremoving the ion line in a television tube operating with a combinedelectrostatic and electromagnetic deflection, one encounters thefollowing difficulty: The cathode ray, in its rest position, after beingdeflected back to the centre of the screen by the D. C. com-- ponent ofthe current to the deflecting coils, does not any longer move along thetube axis. In the space between the deflecting plates and the screen thepath of the ray is inclined by a certain angle with respect tothe axis,Therefore the various positions of the ray are no longer symmetricalwith respect to the marginal field of the main deflecting system,especially that between the deflecting plates 4-5 and the wall coating 3provided inside the tube on the glass wall 20 within the neck and/orbulb portion facing the screen I5 of the tube for removing undesiredwall charges.

In operation, if the cathode ray is acted upon only by the electrostaticmain deflection, the straight line a of Figure 1 passing'through thecentre of the picture area, is drawn on the screen- I5. When thepredefiecting system is caused to operate, there results not only thedesired shifting of this line towards the edge of the picture area, butthe formerly straight line is circularly curved, substantially as shownby line b of Figure 1. Further the luminous spot is greatly distorted atthe points of largest deflection. The widening of the spot can go so farthat, when the intensity of the ray is controlled by means of anet-shaped electrode, the single partial rays passing through the meshesof the net, are visible at the ends of the line b. The just mentioneddisadvantage remains existing even when the electron ray is directedback to the center of the screen by the above described magneticdeflection, since the ray no longer enters the main deflecting space ina central position.

The method as described in the foregoing for eliminating the black lineis practicable only if the neck portion of the tube is made unusuallywide or if the auxiliary plates l2 as well as the deflecting plates 45project into the enlarged front part of the tube body. The auxiliaryplates -I2 must be arranged at least at the joint of the cylindrical andthe conical part of the glass body. This condition, moreover, is known,for the case that a double electrostatic deflecting system is used. Whena combined electrostatic and electromagnetic deflecting system isprovided, however, an arrangement of this kind involves considerableimpediments in manufacture since it is difiicult to conduct the magneticdeflecting field from outside the tube exactly to the desired place, i.e., the space of the deflecting plates 4-5 which latter preferablyconsist of magnetic material and serve at the same time as pole piecesfor the deflecting magnets.

According to the invention, the above described difficulties arecompletely eliminated by providing a separate auxiliary magnetic fieldfor again deflecting the electron ray back to the axial direction, theray being first deflected by the predeflecting condenser I-2.

In a preferred embodiment of the invention the auxiliary magnetic fieldis superposed to the electric field of the predeflecting condenserconsisting of plates I and 2, in such a way that the lines of force of'the electric and magnetic field are substantially perpendicular to oneanother, and that both fields act upon the corpuscles forming the raysubstantially at the same time and within the same space.

The auxiliary magnetic field is produced by two coils 8 and 9 mountedoutside the tube, and is limited to a definite space along the path ofthe cathode ra by means of pole pieces 6 and I mounted inside the tubewall. The length as well as the strength of both the electric and themagnetic field can be adapted to one another by trial.

When both fields are suitably adjusted, the simultaneous influence ofthe electric and ma netic field causes a nearly rectilinear path of theelectron ray through the auxiliary deflecting system while the ions areaffected substantially only by the electrostatic field, the extent andstrength of which are so dimensioned that the ions are deflected out ofthe picture area.

Preferably the longitudinal extent of the ma netic field which can bgoverned by suitably forming the pole pieces 6 and I, is ade as sma l aspossible in order to avoid a disturbance of the electron ray within themain lens caused by the magnetic stray field.

In the circuit shown in Figure 2, l6 represents the low voltage powersupply, I! the television receiver, I8 the high voltage power supply,and

I9 the time base oscillation generator. In Figures 3 and 4, furtheradditional measures are represented which may be necessary for obtainingan unobjectionable efficiency of the device. It is useful to compensatethe marginal field of the predefiecting condenser in its outer space.For this purpose a further pair of auxiliary plates I I--I2 is providedwhich are arranged parallel to plates I and 2 and are furnished withsuitable potentials for producing opposing electrostatic fields.Preferably plate II is electrically connected inside the tube with plate2, and plate I2, in a corresponding manner, is connected with plate I.Opposing fields for com pensating the marginal field of thepredeflecting condenser, of course, can also be produced in other ways.For example, instead of plates II and I2, narrow metallic strips,arranged at the entrance and exit edges of the predefiecting condenserand provided with suitable potentials with respect to plates I and 2,can be used.

In Figure 4, I II is a magnetic yoke provided with magnet poles 2l-22supporting coils 8-9 and being supplied with pole pieces. This part ofthe arrangement is mounted outside the tube wall 20. Element I3 is thereproducing lens anode having an aperture [4, viewed from the side ofthe screen. The pole pieces 6 and I arranged inside the tube wal1 aresuitably shaped and may consist, for example, of iron-plate boxes.Preferably they are electrically insulated from plates I and 2.

The advantage of the described arrangement lies in the fact that thespacing between plates I and 2 need not be substantially larger than thediameter of the cathode ray within the predeflecting space. In this waythe necessary longitudinal extent of the electrostatic fiield at a givendeflecting voltage, or the necessary deflecting voltage at a givenlongitudinal extent of the field, are minimized. The expendituderequired for producing the additional magnetic field is insignificantsince the magnetic field in'questlon is a static one. The necessarynumber of amperetums can be obtained by providing a large number ofturns for coils 8 and 9 but using a current of low intensity which maybe taken from the high tension power supply.

In a modified embodiment of the invention which is illustrated by Figure5, the electromagnets are replaced by a permanent steel magnet 23 havingsuitably shaped narrow magnet poles 21-22 and being provided with amagnetic shunt 26 for adjusting the field intensity.

The arrangement as described at the same time makes it possible to shiftthe picture area in a vertical direction without further additionalmeans, in order to adjust the position of the picture area with respectto the image window of the television receiver case.

I claim:

1. In a discharge tube arrangement a cathode ray tube comprising aluminescent screen, means including a cathode and an anode for producinga corpuscular ray consisting of negatively charged particles and forfocusing said ray on said screen, a deflecting system arranged betweensaid anode and said screen and comprisin' g a pair of magnet coils, fordeflecting said ray in two mutually perpendicular directions, a pair ofdeflecting plates mounted inside the tube between said anode and saiddeflecting system, means for an the more remote plate of said pair ofplates, for

plying a constant potential diiierence between the plates or said pairor such an amount thatthe ions or said my after emergence from the spacebetween said plates are directed out of the picture area oi. saidscreen,'means including a permanent steel magnet mounted outside saidtube and a pair of pole pieces mounted inside said tube for producing aconstant magnetic field substantially within the spacebetween saidplates of such an intensity that the electrons of said ray in thestationary position of said ray impinge upon the centre of said screen,and a variable magnetic shunt for adJusting the strength of saidconstant magnetic field.

2. In a discharge tube arrangement a cathode ray tube comprising aluminescent screen, means including a cathode and an anode for producinga corpuscular ray consisting of negatively charged particles and forfocusing said my on said screen. a deflecting system arranged betweensaid anode and said screen and comprising a pair of magnet coils. fordeflecting said ray in two mutually perpendicular directions, a pair ordeflecting plates mounted between said anode and said deflecting system,means for applying a constant potential difference between the plates ofsaid pair or such an amount that the ions or said ray after emergencefrom the space between said plates are directed out of the picture areaof said screen, at least two further electrodes mounted adjacent to andparallel with the entrance and exit edges or said pair of plates, meansfor connecting each or said further electrodes with compensatingthemarginal field of said pair of deflecting plates, and means forproducing a constant magnetic-field substantially within the 7 spacebetween said plates of such an intensity 1..

that the electrons of said ray in the stationary position of said rayimpinge upon the centre 01 r said screen. I

3. In a discharge tube arrangement a cathode ray tube comprisingaluminescent screen, means I including a cathode and an anode forproducing a corpuscular ray consisting of negatively charged particlesand for focusing said ray on said screen, a deflecting system arrangedbetween said anode and said screen and comprising a pair of magnetcoils, for deflecting said ray in'two mutually perpendicular directions,a plates mounted inside said tube between said anode and said screen,mea for applying a constant potential difierence be con the plates ofsaid pair of such an amount that the ions variable magnetic shunt foradjusting the strength of said constant magnetic field.

FRIEDRICH WOERNER,

of deflectin

